August 2014

Generally in an electric circuit, the rate of energy flow in a specific point of the circuit is called power. In Alternating Current (AC) circuits, there are energy storage elements such as capacitance and inductance which can periodically reverse the direction of energy flow. Active Power (P) is known as the part of power that […]

Per unit quantities, like percentage quantities, are actually fractional quantities of a reference quantity. These have a lot of importance as per unit quantities of parameters tend to have similar values even when the system voltage and rating change drastically. The per unit system permits multiplication and division in addition to addition and subtraction without

The main network components of interest are the transmission lines, transformers, and synchronous machines. (a) The conductors of a transmission line, being passive and stationary, do not have an inherent direction. Thus they always have the same positive sequence impedance and negative sequence impedance. However, as the zero sequence path also involves the earth wire

The following assumptions are usually made in fault analysis in three phase transmission lines. All sources are balanced and equal in magnitude & phase. Sources represented by the Thevenin’s voltage prior to fault at the fault point. Large systems may be represented by an infinite bus-bars. Transformers are on nominal tap position. Resistances are negligible

Unbalanced three phase systems can be split into three balanced components, namely Positive Sequence (balanced and having the same phase sequence as the unbalanced supply), Negative Sequence (balanced and having the opposite phase sequence to the unbalanced supply) and Zero Sequence (balanced but having the same phase and hence no phase sequence). These are known

The currents flowing in the power system network during a fault is dependent on the machines connected to the system. Due to the effect of armature current on the flux that generates the voltage, the currents flowing in a synchronous machine differs immediately after the occurrence of the fault, a few cycles later, and under

The fault analysis of a power system is required in order to provide information for the selection of switch-gear, setting of relays and stability of system operation. A power system is not static but changes during operation (switching on or off of generators and transmission lines) and during planning (addition of generators and transmission lines).

CLR is a well-known fault current limiting technique. Compared with many other methods, it is more economical. In addition its effect on the reliability of substation is negligible. However, it occupies a relatively large area in the substation, due to safety considerations. More- over, it may degrade both voltage stability and transient stability of the

Following are some techniques using for limitation of short circuit current. 1. CURRENT LIMITING REACTORS CLR is a well-known fault current limiting technique. Compared with many other methods, it is more economical. In addition its effect on the reliability of substation is negligible. However, it occupies a relatively large area in the substation, due to